A NATO strike intending to hit Taliban fighters in Afghanistan instead killed four civilians Monday night, an Afghan official told the Associated Press on Tuesday. NATO is investigating the strike, saying it “takes all allegations of civilian casualties seriously, and is assessing the facts surrounding this incident.”

The attack from the NATO helicopter targeted Taliban militants who had missile launchers, the official said. The Taliban fighters fired a missile near an airport in Afghanistan’s Herat province, which drew fire from the NATO helicopter, Herat provincial police spokesman Raouf Ahmadi told the AP. Ahmadi said two men, one woman and a child were killed in the NATO strike. 

A protest erupted in Herat that was attended by 200 people following the strike. 

Civilian deaths in Afghanistan have been on the rise since U.S. and international forces launched a war against the Taliban in 2001. In the first six months of 2014, civilian deaths increased 17 percent over the same period in 2013, according to the United Nations. Insurgents caused 74 percent of the civilian casualties, pro-government forces 9 percent, government forces 8 percent and foreign forces 1 percent.